1. Field of the Invention
The present invention relates to an optical filter apparatus loaded in a broadcasting video camera or the like and, more specifically, to an optical filter apparatus which rotates a filter loading disk having a plurality of filters so as to position a desired filter onto an optical axis of a color separation prism.
2. Description of the Prior Art
In a broadcasting video camera or the like, white light carrying captured image information is separated by a color separation prism into three color light components of R, G, and B, which are then received by CCDs so as to form an image. Also provided is an optical filter apparatus in which a special effect filter such as ND filter, CC filter, or infrared filter is disposed in front of the color separation prism so as to adjust the quantity or characteristic of light incident on the color separation prism according to the circumstance under which the image is captured.
The configuration of a conventional optical filter apparatus will be explained with reference to FIGS. 3 and 4. FIG. 3 is a cross-sectional view showing the configuration of the conventional optical filter apparatus, whereas FIG. 4 is an enlarged view showing the configuration of an axis member which will be explained later.
As shown in FIG. 3, provided in front of a color separation prism 26 in which three prisms 26B, 26G, and 26R are cemented together is a filter disk 28 in which a plurality of filters 29 are disposed around a rotation axis X thereof. The filter disk 28 comprises a disk holder section 28A and a bearing section 28B. An axis member 30 made of a metal having a flange portion is fitted into the bearing section 28B, allowing the filter disk 28 to rotate and slide around the axis member 30. Formed at the tip portion of the axis member 30 is a male screw 30A. As the male screw 30A engages with a female screw 21A formed in a prism housing 21, the filter disk 28 is rotatably attached to the prism housing 21.
A gear section 28C is formed around the bearing section 28B of the filter disk 28, whereas a driving knob 31 for rotating the filter disk 28 is attached to the prism housing 21. A gear 32 attached to a rotation axis 31A of the driving knob 31 and the gear section 28C of the filter disk 28 engage with each other by way of an idle gear 33. Accordingly, as the driving knob 31 is rotated, the filter disk 28 rotates around the center axis X of the axis member 30.
Thus, the filter disk 28 is rotated so as to position the desired filter 29 onto the optical axis of the color separation prism 26, whereby the quantity or characteristic of the light incident on the color separation prism 26 is adjusted.
In the foregoing prior art, however, in addition to the main body of the filter disk 28, the axis member 30 which is fitted into the bearing section 28B thereof is necessary, thereby increasing the number of parts. Also, when assembling the apparatus, a step for fitting the axis member 30 into the filter disk 28 and engaging the axis member 30 with the prism housing 21 is necessary, thereby increasing the labor required for manufacture. Consequently, the cost for making a video camera adopting the optical filter apparatus has increased.
Further, as shown in FIG. 4, since fitting length L2 between the bearing section 28B of the filter disk 28 and the axis member 30 is not so large, there may occur fluctuation in rotation when the filter disk 28 is rotated, such that the filter 29 is obliquely positioned with respect to the optical axis of the color separation prism 26, thereby deteriorating the optical performance of the filter 29. Also, the peripheral portion of the filter disk 28 may rotate while abutting to the prism housing 21 disposed in front of and behind it, thereby wearing off, yielding a powder of wear dust, which may adhere to the filter 29 or the color separation prism 26.